This invention relates to a signal detecting circuit for an electronic musical instrument in which an acoustic vibration is picked up to generate an electrical signal which is used as the input signal to drive the electronic musical instrument.
An electronic musical instrument of this type, such as a so-called guitar synthesizer is provided with a function to trigger off a musical tone in accordance with the external vibration signal and a function to store and hold the external vibration signal (such as a string vibration signal) so that, even after the vibration of a string has been stopped, the musical tone can be produced.
These functions are obtained for instance in the following manner: First, the vibration of a string is detected by a pickup to provide an electrical signal, from which the fundamental wave is extracted, and a voltage signal corresponding to the frequency of the fundamental wave is provided. Then, the voltage signal thus provided is stored in a capacitor or the like, so that a voltage-controlled oscillator is driven by the voltage signal thus stored, thereby to produce a musical tone signal having a frequency corresonding to the relevant string. A timing of flipping the string is detected according to the aforementioned electrical signal to provide a detection signal. Then, this detection signal is used as a trigger signal to produce a series of control waveforms from a control waveform generator or the like. The control waveforms are used to drive a voltage-controlled filter and a voltage-controlled amplifier, so that the musical tone signal is subjected to tone color control and amplitude control for production of a musical tone.
In the electronic musical instrument of the type described above, the detection of the above-described flipping timing plays an important role, and it is necessary that, even if the string is flipped in succession, the trigger signal should be provided positively at each flipping of the string.